1. Field of the Invention
The present invention relates to processing of signals in network environments. The present invention relates to an implementation of burst mode receiver that receives packets in a bursty mode with possible idle periods between sequential receptions. The functionality of burst mode receiver related in this invention is to lock on the incoming signal, and recover the clock and the data from the signal. In particular, the present invention relates to the use of such burst mode receiver in high-speed (such as 10 Gbps or 40 Gbps) optical systems, cross-bar switches and all-optical networks.
2. Description of Related Art
Fiber-optic infrastructure is a vital part of today's rapidly changing worldwide networks. The drive for interconnectivity as well as the exponential growth in data traffic, as a result of new applications, requires the adoption of new solutions and in particular optical routing solutions that embody routers that handle optical packets. These new generation optical routers must be able to handle terabytes of data that arrive from different sources in a burst-mode, and multi-layer routing structure based on DWDM optical. In order to handle burst-mode traffic, the optical router should be capable of transmitting bursty packets to the destination routers and receive bursty packets from the source routers.
A vital component in an optical router is a burst-mode receiver (BMR). That component receives fixed-size or variable-size packets at high-speed, in burst-mode with possible unknown idle periods between sequential receptions, and recovers the clock and the data from the signal. Generally, a clock and data recovery receiver, (CDR), that is not locked on an incoming signal requires a period of active signal before it is capable of extracting a correct clock and data from the incoming signal. This period is called the receiver “locking time” or “acquisition time”.
In continuous systems, the transmitter sends packets continuously to the receiver, and thus the receiver requires a single locking time to lock on the incoming signal when it first appears; after that it stays locked, assuming that the signal arrives without interference. In case that the transmitter does not have packets to transmit, it still sends dummy sequence to keep the receiver locked.
In a burst mode system, the transmitter sends the signal in bursts, and thus on the start of each burst of data, the receiver requires a locking time to lock onto the signal. Since during the locking time the receiver cannot extract a valid clock and data, the transmitter starts each burst with a preamble sequence for a locking time. Thereafter, the data itself is sent. Usually a preamble sequence is “101010 . . . ” since this is the easiest pattern to lock on.
In the burst mode system, the preamble sequence that lasts for the duration of the locking time is a wasted transmission time since it does not carry a valid data. Thus, in order to achieve high performance system, the locking time is minimized as much as possible. Burst mode receivers are receivers which have locking times that are much shorter when compared to continuous mode receivers.
Burst mode receivers can be classified to two groups: over sampling clock recovery, and non-over sampling clock recovery. Over sampling clock recovery receivers are based on the concept of sampling each bit the incoming signal several times with a higher speed sampler and detecting the transitions in the samples. The advantage of such receivers is that their locking time can be very short. However, since such receivers require over sampling of at least four samples per-bit, this kind of receivers is limited to low speed systems (below 1 Gbps). The use of such receivers is popular in the PON (passive optical networks) standard which operates at 622 Mbps. In high-speed systems, such as 10 Gbps or 40 Gbps systems, these kind of receivers cannot be used since it requires 40 G or 160 Gbps sampling rate which is very hard to implement and may not possible with today's technology. In addition, this method requires that the receiver and the transmitter clocks will be close enough to achieve a proper lock.
For such faster networks, non over sampling clock recovery receivers, which are capable of reaching 10 Gbps and even 40 Gbps line rate, are of greater interest. Thus, there is a need in the prior art for a burst mode receiver that has a reduced locking time without increasing noise in the recovered clock and less prone to loss of lock after the lock has been obtained.